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If Space Shuttle flies "like a brick", why does it need the wings?
I have seen the Shuttle named a "flying brick" multiple times.  However a brick, as understood in the building industry, is a simple rectangular shape without wings and without any adaptation of the form. If the Shuttle was only capable of that much, why could not it be a lifting body like  Martin Aircraft X-24?

Wings actually gave the shuttle a better glide ratio than lifting body designs. I'd suggest looking on Space Exploration SE, there's already QA about this subject there.

I recall reading that it glided like "a cast iron Frisbee".  Also like a brick, of course.  For comparison, the orbiter had about the same glide ratio as a skydiver in a squirrel suit -- but had to fly about twice as fast to stay above stall.

Comparison of the shuttle wing design to a lifting body is a legit question, but I am downvoting on the basis of the main question as it is worded now.

@h22 the Martin X-24 (and the modern Dreamchaser) are much smaller.  There for, their weight to lifting area ratio is significantly different.  Same reason you can't scale a delta paper airplane up to a 747 (unless it goes much faster).  Not a bad question, but flying faster than the Shuttle would not be easy.

Bear in mind that during the landing flare, the Shuttle, like all aircraft, is briefly in a very shallow - almost flat - glide. Bricks don't do that.

Because "flies like a brick" is preferable to "falls like a brick".

You don't think bricks would fly better if they had wings?

Rule of Cool...

I think we need to introduce you to the concepts of "metaphor" and "humour", Mister Data...

@AnthonyX If they were moving fast enough and had flight controller surfaces, maneuvering thrusters, or some other method of controlling their roll and pitch attitude, then bricks could indeed flare. Lifting bodies generate more lift at high AoA, too, not just wings. Boeing recently had some issues with this...

Possibly a loose allusion to "The ships hung in the sky in much the same way that bricks don't". - Douglas Adams. I've often seen quotations from from surreal scifi/fantasy authors referred to in engineering-related texts, both serious and non-serious.

@Rodney the thing that makes that statement humorous is that "falling like a brick" is an old and well-understood concept.

It should be noted that if it kept a proper angle of attack, a brick at Mach 26 would generate a noticeable lift.

The small wings make it fly like a brick. Without the wings it would fly like a stone.
Seriously, you are taking the expression too literally. The Space Shuttle is landing like a glider plane with a (not so good) glide ratio of about 4.5:1 (see What was the Space Shuttle's glide ratio?). No brick would be able to achieve that.
Designing the Space Shuttle as a lifting body ( ≠ brick) was actually considered. It appears that a lifting body design was not able to comply with the flight envelope requirements.

Bearing in mind that the Shuttle flares onto the runway like any other aircraft; the landing flare for the Shuttle is the same as for any other aircraft - a very shallow glide.

Also, it's always been my understanding that the "flies like a brick" description was more of a reference to its handling than to its glide ratio: you may cover more horizontal distance per unit of altitude drop than a brick would, but if you're the guy behind the controls, and you're accustomed to much more maneuverable vehicles (shuttle pilots have mostly, if not entirely, been drawn from fighter pilots), then the way it feels as you try to get it to go where you want it to, is gonna feel very distinctly brick-like.

To extend @MatthewNajmon's comment, you often see similar descriptions of cars, e.g. "handles like a boat" which means a wide turning circle and/or not a good steering response. The SS flying like a brick is almost the exact equivalent of a car handling like a boat.

Don't forget that the space shuttle flew Mach 25 at up to 45 degrees of angle of attack... any more wing span would probably cause significantly more stress and thus increase weight, weight that takes away payload capacity. The low glide ratio is actually not too bad for reentry, enough to have a shallow descent angle and thus reduce the g-loads and not too shallow to bounce off the atmosphere

As everyone has pointed out, it's a joke. Others have answered the lifting-body question (it didn't meet design requirements), so I just wanted to expand some thoughts on the spirit of the "flying brick" nickname.
I suspect whoever came up with the term didn't spend a lot of time analyzing it. However, I think it's significant that the nickname is flying brick - not falling brick. It doesn't imply that the shuttle doesn't have wings or can't fly. Instead, it implies that the vehicle has blunt and non-smooth surfaces which creates tremendous drag (like a brick) and limits its glide ratio.
For my talk on how to land the space shuttle, I created this visual, which I think captures the spirit of the nickname:

Unfortunately, even though I think you knew this was a joke, a lot of people take jokes and analogies too seriously and turn them into conspiracy theories. I get lots of comments on my talk from people who think that, if the shuttle flies like a brick, it can't possibly be a glider and therefore... space is fake. ♂ (/facepalm) So... I don't think having serious answers to a question like this is a bad thing.

What is the "♂" supposed to mean?

@sean that unicode didn't render for me either, so I googled the three characters together, and the top match says https://emojipedia.org/man-facepalming/  or  https://emojipedia-us.s3.dualstack.us-west-1.amazonaws.com/thumbs/120/emojidex/112/man-facepalming_1f926-200d-2642-fe0f.png

@Criggie: How did you get all that from two empty boxes and a male sign?

@Sean I copied and pasted his 3 characters into google.  Try it for yourself

It's a face-palm emoji. Hard to describe my feelings on the subject better.

@Sean Most likely a combining-character emoji that only renders on certain platforms. On Firefox Linux I see a facepalm and the male sign. (Just one more reason to loathe emoji...)

Chrome on Linux - just the facepalm.

Interestingly, I have the opposite experience - the combined character appears in Firefox, but in Chrome I see the "broken" three characters (a ghostly facepalm, a square box, and a masculine ordinal sign). I think it must depend which font(s) happen(s) to be used.

@BretCopeland: Emojis are pretty small at a normal font size for stackexchange; I saw Sean's comment before I figured it out even though it rendered correctly (Linux/Chrome).  IDK how quickly I would have got it after leaning in a bit closer to see more clearly (I sit pretty far from my monitor).
Anyway, I'd just write /facepalm to express that sentiment, I can't be bothered to use emojis when English is such a rich language and fast to type.  (I used to play World of Warcraft where /emote commands like that made your character do stuff, but it also works by analogy to IRC commands.)

In addition to its poor glide ratio the shuttles name also stems from the materials its made from as much as it does its poor glide performance. The Space Shuttle's heat shield was made out of LI-900 Silica tiles that strongly resemble bricks and thus the shuttle was sometimes called the "Flying Brickyard".
If you would like to know why NASA chose a wing design over another capsule or lifting body they actually published an explanation here as to their choices. In short it was a mix of socio-political pressures and old school "airplane" mentality where many of the engineers came from, a large chunk of Air Force requirements driving the original designs and hard engineering reasons that lead to the Delta Wing vehicle that was ultimately built.
In response to the other portion of your question, A lifting body could be used and that is basically the design of Sierra Nevada Corporation's new Dream Chaser.

I dispute your misnomer theory. the "fly like a brick" joke has always been a reference to its poor gliding ratio, to me.

@Federico I guess thats the wrong term to use, call it "another reason why" but i agree ill remove the first sentence. -- Edited---

Excellent link to NASA's explanation! But I don't see how you come to summarize it as socio-political and airplane mentality. The article is listing a number of hard engineering requirements that couldn't be met.

@bogl did you click through the links at the bottom of the page to the other sections? There was some prior winged craft design experience. The project was also in part driven by Air Force requirements. It was a mix of a lot of reasons including engineering ones.

The Dream Chaser is a project of Sierra Nevada Corporation, not NASA.  And if you look at the pictures, it does have quite obvious wings :-)

"Flies like a brick" is merely a figure of speech. It comes from personal feelings of the pilot when comparing it to an actual plane.
It's just like the saying that someone is "dumb as a rock". Obviously, even the most stupid person (or even animal) is much smarter than rock. The saying merely expresses the frustration of the speaker when dealing with a person that stupid.
"Flies like a brick" was coined most likely because of combination of its abysmal glide ratio (1:1 at its worst, 4.5:1 at it's best) with simultaneous (and counter-intuitive) reliance on it. Compare it to a 747 which has quite poor glide ratio of 17:1 and it's not supposed to glide. Sailplanes have over 50:1, so that's the kind of performance a sane person would expect from a vehicle that's meant to do nothing but glide.
An actual brick has glide ratio of about 1:10. In fact, the Space Shuttle flies more like the best sailplanes (11× difference) than like a brick (45× difference). Surprisingly, it's marginally better than Concorde at take-off (4:1), but not at speed (12:1).
I couldn't find the glide ratio of an X-24, but it must have been considerably better than 1:1 (to be considered flying instead of falling), so that's still more than 10× better than a brick.

Adding to other answers, yes space shuttle is a brick that flying not just a brick. Body-lifting can not be disregarded in hypersonic flight during the reentry, it is not just the wing creating the lift, it is the whole bottom section hitting the atmosphere.
Looking at another famous spacecraft, Appollo, it doesn't have any conventional wings but NASA uses only CG shift and altitude control to achieve atmosphere skipping because the body lifting from its bottom side. This documentary explains how it is done:

The wing also gives the shuttle huge landing flexibility, or what called the "cross-range" which brings to my third point.
Changing direction in orbit takes a crazy amount of energy and in orbit, you are on "rail" sort of speak. The Earth rotates below you and to return you have to wait until you got a close passage across your landing site. However, with Shuttle's relative big wings, it has a huge of cross-range(it is actually a design goal originally from the Air Force), the shuttle can make big direction change during reentry just like a normal airplane. It has about 1100 nautical miles in cross-range, which means the closest approach to Cape Canaveral could be as far out as in the middle of the Atlantic Ocean and still be able to glide back.


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Why does the 757 fuselage bend more on turbulence than those of other airplanes?
According to this discussion(2nd)(3rd) and this video there is more fuselage bending in turbulence on the Boeing 757 than on other Jets.
Why does the B757 fuselage bend more on turbulence?
What are the factors related into fuselage bending?
I always thought there is only fuselage bending during take-off and landing on tarmac.

Edit: Picture Zoomed, fuselage shows flexing.

Other type of bending due to hard landing, worth a look: https://www.youtube.com/watch?v=S7pXjQ16f5c

The YT vid looks much like when I try to lend in the FlightGear amateur simulator, and it looks pretty scary!

What is the arrow in your first picture supposed to indicate?

I'd rather have it flex than snap, personally. Maybe that's just me. Also, the line wrapping on the 'popular questions' list made me think fuselage and factors were a single word and I read "why 757 fuselage has more turbulent bacon" and was immediately interested.

how do you know from that video that it's the fuselage flexing and not the seats/floor panels?

The lower picture shows panels in the lower aft fuselage buckling. This is normal under load (and hard to pick out even in the zoomed version).

@PeterKämpf But this photo shows identical patterns on the lower aft fuselage on final approach which presumably isn't anything like as stressful as take-off. Is it buckling under load or just that the panels in that area are a bit beaten up?

@DavidRicherby: In both cases the flaps are down and the tail produces a considerable downforce for trimming. I would wager to say that the load in your linked photo is even higher and causes this buckling. I would expect that the buckling disappears both when the aircraft is in cruise and when it is on the ground.

@Johnny You're right, that video isn't showing fuselage flexing. (Not that it couldn't be flexing, but the video isn't evidence of it.) Those are interior plastic panels that are more-or-less loosely attached to the actual structural fuselage across a significant air gap.

I dare say the Concorde flexed more... https://books.google.com/books?id=lpiMSzja6W4C&lpg=PA142&dq=concorde%20flexing&pg=PA118#v=onepage&q=concorde%20flexing&f=false

This is really two questions

Why does a fuselage bend?
Why does the 757 fuselage bend more than others

I'll give the simple answers here. You can go into a LOT of detail, but the detailed answers are mainly just bringing more information on design/engineering differences into the simple answers (eg composites bend/break in a different way to aluminium)
Why does a fuselage bend?
Essentially, it's because the lifting force doesn't support the entire fuselage equally. Drag and the aerodynamic forces created by the fuselage itself will also affect things, but it's mainly due to the fact that the lifting force is centred on two points of the fuselage, while the weight is spread along it
The lift is generated, primarily, in two places: the wings and the horizontal stabiliser (some is generated in the body too, but relatively little). Most of that lift is generated at the wings, which are attached in the middle(-ish) of the fuselage. Imagine balancing a ruler (fuselage) on your finger (wings), then stacking coins along the top of the ruler. The heavier the rule, and the more "lift" your finger has to provide, the more the ruler flexes.
Of course, lift isn't constant - turbulence means that over a few second the lift provided by the wings can change quite a lot. Imagine you start bouncing your finger up and down, creating "turbulence": the ruler will flex and unflex as it absorbs that changing force. This is the fuselage flex seen in aircraft.
The fuselage will also bend while landing or taking off, because you're again changing how the weight of the fuselage is supported: the weight is transferred from the wing root/spar to the landing gear. And the final obvious one is that the weight of the aircraft changes during the flight due to fuel burn etc.
Why does the 757 flex more than other airliners?
Well, for one thing I don't see any sources for this other than "I've heard that" (the links you provided are mostly hear-say too), but I have seen it stated as fact. Let's, for the moment, assume it's fact... the theory applies regardless.
The 757 will flex more than some other airliners (although likely less than some others) because of its design, construction and the build materials. The simplest explanation is that it's one of the longest narrow-body airliners.
What does that mean? Well, it means it's one of the longest, thinnest fuselages around. This gives us two causes:

The 757 flexes more than other large airliners because anything bigger than it is a wide-body aircraft, which will resist bending more than a small, narrow bodied thin one
It flexes more than other small airliners because any other narrow body is lighter and shorter than the 757, providing less force on the fuselage and requiring a smaller lifting force.

TL;DR: Flex is caused by lift acting mostly in the middle(ish) of the fuselage, while the weight of the fuselage and other forces on it are spread out along the length.
Overall, then, the 757 is on the boundary between lighter, narrow bodied aircraft and larger, wide bodied ones. Anything smaller than it weighs less so stresses the narrow body less. Anything larger has a bigger, stronger fuselage.

First, there is no fuselage bending to be seen in the linked movie. What might look like flexing is actually the seats and the interior panels moving due to inertial forces. In turbulent weather the aircraft will be shaken by gusts, and this causes the movement between seats and panels.
Second, in the picture the flaps are in take-off, shifting the center of lift aft, and the tail pushes the nose up, so it needs to create a considerable downforce. This is transferred via the rear fuselage to trim the moments of wing lift and weight, which attacks at the center of gravity. See the sketch below; blue are aerodynamic forces and red the stresses in the fuselage.

Your enlarged picture shows buckling of the lower rear fuselage panels. This is normal behavior under stress and enables them to take higher loads. When a plate is stressed, it first deforms in-plane, but when compression loads exceed a critical value, the plate responds by buckling out-of-plane. The sketch below shows the general relation between stress and strain.

For the 757 flexing more than other airplanes: Maybe this has to do with the slender forward fuselage. This leads to more flexing at the same strain in the aluminum panels. The rear fuselage is higher to accommodate more baggage. During development Boeing engineers were afraid that directional stability might be insufficient with a higher forward fuselage, so the cross section was restricted to that of a Boeing 737. But there are aircraft with even more slender fuselages like the MD-90 (see below). They should flex at least as much as the 757.

Any aircraft part will flex when subjected to stresses, and the fuselage is no exception. Especially the forward part will create lift and side force during flight, its own mass will cause it to bend down the more you move away from the wings, especially when subjected to g-forces, and tail-mounted control surface deflections will add more stress and bending, like in your picture. Fuselage flexing is actually severe enough that in flight test the fuselage will carry inertial sensors at several locations to collect enough data.

Note that (hopefully), the fuselage itself will never go into buckling mode, but will only be stressed in the linear part of the stress-strain diagram. The only things buckling are the decorative panels.

@sanchises: Those panels take shear loads and help the (indeed hopefully non-buckling) longerons to be loaded with compression and tension loads. They are an integral part of the load-carrying structure!

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Why is port-starboard terminology used in aviation?
I am not a pilot - just a student & play Ace Combat sometimes
Intrigued by the words Starboard & Port-side, I researched why these words are used instead of the simple ones, I found that:

Port is derived from the practice of sailors mooring ships on the left side at ports in order to prevent the steering oar from being crushed. src

Also, quite notably:

Since port and starboard never change, they are unambiguous references that are independent of a mariner’s orientation, and, thus, mariners use these nautical terms instead of left and right to avoid confusion. When looking forward, toward the bow of a ship, port and starboard refer to the left and right sides, respectively.src

I see both the reasons are derived upon the concerns of the marine world - so why do we use them in the aviation world?
This is specially interesting if we consider the fact that flying machines can maneuver in all 3D, newbies (me) tend to lose track of my VS. plane's left & right when not in level flight. Then why the added confusion?

in non level flight port and starboard are usually still in the same place, it's only when you go inverted that it's more confusing.

Related: Viking steering boards and terminological conservatism - Also, navy aviators don't use these terms for obvious reasons.

I have never heard port and starboard used in aviation.  Airfast 123, turn left heading 350 degrees.  Airfast 123, traffic 4 miles, same level crossing left to right.  Airfast 123 exit the runway 3rd exit on the left.

@Simon It's used "internally" as in port engine, starboard landing gear etc.

@Sami  Where?  I worked in military maintenance (RAF and BAe) for 20 years and never used port and starboard.  Left engine(s) were called left and number 1 or 1 and 2 for 4 engined craft. We always referred to left and right gear etc,  The Boeing and Airbus checklists I can find with a quick search all refer to left and right or engine number,

@Simon can't say how common or uncommon it is. Certainly i have heard someone use the phrase somewhere. Unfortunately didn't make a note.

@Sami i echo Simon's comment for commercial ops.  "Engine #1" or the "right main gear", or the "left pack", etc is how we referred to things to everyone including maintenance.  Maintenance logbook entries likewise would say things like "serviced oil #2 engine".  No use of port or starboard to be found anywhere.

Same here. We number things left to right when there are more than two (engines, etc) and even sometimes when there are only two. I've never heard the terms actually used in aviation in all my years of private and commercial flying, and many pilots would be confused if you used the term and not even know which side is port.

Your, and your plane's, left and right are the same whether you are upright or inverted.  It really isn't confusing...  (It is the compass cardinal directions that might get mixed up)

OK, I meant flying in a real airplane it isn't confusing.  I could see how flipping the plane on a simulator screen while maintaining an external view could get confusing.

@RedGrittyBrick -- re "Also, navy aviators don't use these terms for obvious reasons." -- what obvious reasons?  How would the logic for what terms a naval aviator might use, be different, from, say, what terms a captain maneuvering an oil tanker might use?   (Or-- is that what cause this https://en.wikipedia.org/wiki/2021_Suez_Canal_obstruction -- the ship was passing a port, on the starboard (right) side, and the captain said "steer to port" -???)

@quiet flyer: Naval aviators might avoid terms that land-based aviators could use in order to avoid confusion when approaching a carrier for landing. The aircraft's "starboard" might be the same as, or different to, the ship's starboard. You want any communications to be as unambiguous as possible.

@RedGrittyBrick -- I hadn't thought of that.  Thanks.  (And I didn't expect such a fast response to a comment on a six-year-old comment!)

Shuttle used port / starboard terminology frequently. Especially in robotics ops, which sort of makes sense from a reduced-confusion standpoint, because the operators were facing the tail of the vehicle. Here's a robotics switch showing the nomenclature https://imgur.com/a/D9rqO95

It isn't (much).
Ships are the most similar thing to aircraft that existed before them, so it made sense that aviation took over many terms and conventions from seafaring (the pilot in command is called captain, the cockpit is the flight deck, data are recorded in a logbook, distances and speeds are given in nautical miles and knots etc.)
However since there is no physical port in an aircraft to serve as reference (most aircraft have doors on both sides), everybody has to learn to give the sides relative to the direction of flight and then it does not make sense to teach them new words when they already know “left” and “right”. So “port” and “starboard” are only used where there is a naval tradition.
I know British military aviation (RAF) used it (in wartime stories and documents it is common, but according to Simon's comment it is not common any more) and the US Navy uses it with ships, but I don't know to what extent they apply it to aircraft.
However, it remains popular in simulator games, presumably because it is catchy and unusual and using jargon makes people feel special.

Thanks, especially for pointing out remains popular in simulator games, presumably because it is catchy and unusual.

Minor nitpick not really relevant to the answer as such: "Captain" is a rank, in this case an airline rank, just as it is a rank on a ship, and a rank in the military. You can be a captain of the army and never have set foot on a boat. You can still be a captain without being PIC. Sometimes there are two captains up front, but only one of them is PIC. When I fly, I'm the PIC, but I'm not a captain (there is no captain in my case). I'll crawl back under my rock now.

@falstro 'Captain' is also a position of responsibility on a boat or plane. You can be the captain of a boat or plane, even in the military, without holding the rank of Captain. And while 'PIC' is the normal terminology, the position is sometimes also referred to as 'captain'.

My understanding is that naval aviators especially avoid using port and starboard for directions relative to the plane, as they are reserved for directions relative to the carrier they are taxiing, taking off or landing on.

@IanF1 I've never heard anyone specifically avoid using it, its just not very common. As for taxiing, we don't do any of that on our own anyway. Every movement on the flight deck is highly choreographed by our yellow shirts, including the degree to which we move our nose wheels.

"most aircraft have doors on both sides..." If it was the reason, no pleasure boat would use the old wording, they are built symmetrical and moor on both sides at landing stage. This seems more about reusing old-fashioned words, by tradition, like all this fuss about not using some words on board (banana!), and as you emphasized, because this sounds like the speaker is very knowledgeable.

The use of nautical miles and knots has less to do with the shared sailing heritage of flight and more with the practicalities of navigation. They are logical and useful units: One nautical mile is one minute of arc, so sixty nautical miles is one degree of position. If you're crossing an ocean at propeller speeds with nothing but a sextant, a stopwatch, your airspeed, and your charts that direct correspondence is very useful, as it was for mariners who only had a sextant, an hourglass, and a chip log to update their position on the chart.

@ob318, yes, logbook too comes from seafaring, though that word has made its way into other domains as well so I didn't consider that special.

Note that use of “Captain” and naval-style uniforms was a deliberate move by Pan Am to reassure the early passengers on their flying boats that they were a professional aviators, unlike the barnstormers of the era.

The greatest value of port and starboard over left and right is when you have people facing multiple directions. port and starboard are always vehicle centric directions (as are fore and aft) and remain constant regardless of which way you are facing. In this context right and left therefore apply to the people (or other things that have left sides like consoles) in the vessel. Therefore it is perfectly reasonable for a flight attendant to turn left, starboard and north all at the same time. A pilot should not try to do this while working. This distinction is less useful if the craft is not big enough for those inside to move, and more useful when you our vessel is large enough to have a map of the interior.

This makes sense, good point.

This shows up more often in engineering documentation than aircraft operation I've observed.
For example: you sometimes see schematic labels like "STBD NAV LT" (starboard nav light)
This is helpful because when you say "left nav light", a reasonable question is 'whose left?'. PORT and STBD, FORE and AFT completely remove the ambiguity.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@RalphJ I have edited the answer to more directly address the question. Hopefully this answer provides context that others have not.

"This is helpful because when you say "left nav light", a reasonable question is 'whose left?'" I've no difficulty to look at the left wing of an aircraft when standing at the cockpit door. I know it's on the side of my starboard arm.

A lot of nautical terms made their way from naval architecture into aviation.  For instance the vertical coordinate system used in aircraft design is still designated WL for "Water Line", straight out of shipbuilding.  Some habits are hard to break, I guess.

The word "keel" is also used on aircraft...

"However since there is no physical port in an aircraft to serve as reference"... this is not a valid explanation. A ship underway doesn't have a port either. We rely on Vehicle centric Port and Starboard and use left and right with respect to the persons orientation. If a person were standing looking at an aircraft and an engine caught fire and they said over a comm device that the left engine is on fire... how do you know he's not talking about the engine to his left... simple yes, but it does illustrate a point in the nautical term usage.

Actually, they'd refer to the #1 or #2 engine (or the #3 or #4 as appropriate). Backing a C-130, the Loadmaster gave directions as "turn toward #1" or "turn toward #4."  Inside, the usual frame of reference for airline crews is "captain side" or "first officer side" since walking down the aisle, "your" left & right is opposite the aircraft's left & right.  I've never seen or heard port/starboard terminology in aviation, but I've only been doing it for about 30 years total -- there's lots of history that predates me.

@RalphJ It is (was?) used in the Royal Air Force when talking about some equipment, e.g. the port and starboard pitot static vents.  Left and right were not used then as they would be ambiguous.

"If a person were standing looking at an aircraft and an engine caught fire and they said over a comm device that the left engine is on fire... how do you know he's not talking about the engine to his left..." Following your reasoning... in court a witness should be asked to raise their starboard hand and swear to tell the truth, to be sure the facing judge is not talking about the hand on their own right side. Come on, everyone working on aviation industry knows what is the left wing, there is no possible confusion ;-)

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Is the 737NG hydraulically controlled or electronically controlled?
I know that the 737NG is not fly-by-wire, but are the control surfaces controlled with hydraulic systems that transfer the input from the pilot to the control surfaces via fluid (hydraulics), or is the pilots' input transferred to the control surfaces' electronic actuators via electric signals?

"electronic actuators"... electronics and torque are not good friends :-)

For the B737NG, the pilot stick inputs are transferred to hydraulic actuators, via mechanical (steel) cables. For example for the Power Control Units of the ailerons, as also depicted in this question:

The site where the image came from also lists a schematic pic for a fly-by-wire setup. There is still a hydraulic actuator but no more steel cable loop to the extremes of the aeroplane, only an electrical or data wire that sends a signal to an electronic controller near the control surface. The controller measures the surface position, subtracts that from the pilot input position, and deflects the hydraulic valve until the actual surface position = required position.

Of course it's hydraulic.
Electric actuators or power-by-wire is actually a far more exotic technology than fly-by-wire, and the latter is a hard prerequisite for the former.
Normal fly-by-wire is still based on hydraulic systems, with the electrical FBW system controlling the valves. And even in power-by-wire systems, the final actuator is typically a small enclosed hydraulic unit.
The newer 737 MAX has a couple FBW elements (spoilers), but is still a manual system, well short of FBW or PBW.

Mhmmm, how bout on the max? And does that mean that the 737 is less reliable than the a320? Or is it safer as a human is operqting the controls?

By max I meant the 737MAX

Reliability is a complex subject, and safety a further separate one. Statistically speaking, the A320 has a better record. What can be said for sure is the A320 is a much more modern design - the 737 is itself based on the 707.

Yes, true, but why is the 737 still so popular? Its the A320 is so good in every aspect, then why does Ryanair use them?

The economics. The 737 is simpler and lighter, coming out to a slightly lower CASM. But it's got a tighter cabin and can't carry ULD boxes. The two have been close in sales, with A320 edging out ahead lately. You'll have to read a lot of industry publications to get an idea of what the competition is about. The short version is of course money.


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Like transponders, can flight recorders be turned off?
I never knew much about airplanes before the tragic incident of Malaysia 370. I have been spending a lot of time on Twitter reading various articles and investigations; in one of the articles I read, they stated that unlike transponders, "black boxes" cannot be turned off.

However, each ELT is specifically designed for each aircraft, so it
  cannot be tampered with. You also cannot turn off the black box, as it
  runs throughout the flight, recording every 30 to 60 seconds.

Is it really impossible to turn off the black boxes from within the plane?

There is no switch for the FDR, but there is a circuit breaker and by pulling this you are removing aircraft power from the FDR.  However, this does not mean you are necessarily turning it off, as some FDR can be equipped with an internal power supply as a backup to aircraft power.
The quote in the question (bolded emphasis mine):

You also cannot turn off the black box, as it runs throughout the flight, recording every 30 to 60 seconds.

is a case of an "expert" or journalist confusing the lack of an on/off switch as an inability to turn something off.  As you'll find many examples of in the media, they don't always get it right.  The circuit breaker may not be a true on/off switch, but pulling it does accomplish de-powering (assuming no internal power supply) and thus turning off the FDR.

in context to your answer, could you please see this ? http://en.wikipedia.org/wiki/SilkAir_Flight_185#CVR_and_FDR_deactivation

@SufiyanGhori That is just an example of someone pulling the FDR circuit breaker.  As I mentioned in my post, some FDR may have an internal power supply, but I don't have any statistics on what percentage of the installed base does.  For those that dont, just as in your example, it stops recording because it is turned off.

the biggest problem with an internal power supply it that is can fail with potentially catastrophic results

@ratchetfreak I'm not debating the merits of an internal power supply, I'm merely mentioning them to cover my bases in that "pulling the breaker == off" may not be true in 100% of cases.  Certainly in the plane I'm most familiar with we did not have that and if you pulled the breaker the FDR turned off and you got an EICAS message indicating DFDR FAIL.

@ratchetfreak what about in case of MH370 ? because the link aforementioned, clearly claims that it cannot be turned off ?

@SufiyanGhori see the edit to my answer.

On most 777’s, can’t say with certainty on MH370, the circuit breaker is downstairs in the E&E and not accessible from the flight deck.

Generally, I'm pretty sure there's no switch for a Flight Data Recorder on the overhead panel in most aircraft, since I think it switches on automatically. However, i'm pretty sure that you can pull the corresponding fuse behind the cockpit. It's a safety thing after all, since you don't want a short circuit from the FDR causing problems to the rest of the plane.
While I'm not sure of how this works on the Boeing 777 as in MAS370, it was attempted on FedEx flight 705.

I vaguely recall an accident where they concluded someone pulled the breaker for the CVR; so it was certainly possible on that type of aircraft whatever it was. Can't remember which thought. Also, the FedEx flight; but that one got reset, so it was never really turned off.

@roe both breakers can be pulled which is what happened in Silkair Flight 185

Ah, right, Silkair 185 was the one, thanks.

does the b777 have an internal power supply for the FDR?

Neither the FDR CB nor the CVR CB are accessible from the B772 flight deck.  The FDR is powered on at engine start. In the event of a mishap the CVR CB is pulled as a means of saving the data.  The CVR CB is accessed from the E&E bay.

On most commercial aircraft there is a circuit breaker for the cockpit voice recorder. The recorder can record communication in the cockpit for 30 minutes or up to two hours on later model aircraft. They are continuous loops which will record over the oldest previous recordings. Whenever any incident occurs during the operation of a flight, the circuit breaker is pulled to keep the pertinent cockpit conversation on record and not be recorded over. I am unaware of any such circuit for the flight data recorder.

The FDR probably has a CB protecting it, although since modern FDR's can hold weeks of data, there is no need to pull its CB to preserve accident (i.e. recent pre-accident) data as there is with the CVR.


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How much thrust could a 400 mm EDF produce?

There's a 195mm EDF from Schübeler that produces 25 kg of thrust at a peak power consumption of 15 kW: https://www.schuebeler-jets.de/de/produkte/hst
Now, my question is: How much thrust could you approximately get if the diameter was 400 mm instead of 200 and how much more power would you need ?
Thanks for your answers !

It can be safely assumed that thrust $L$ is a function of the input power $P$, the diameter $D$ of the gas jet and the air density $\rho$.
Thus, $L = f(P,D,\rho)$
where $f$ is a function to be determined.
From dimensional analysis, the thrust $L$ can be easily derived:
The variables are Thrust $L$, dimensions $MLT^{–2}$; Power $P$, dimensions    $ML^2T^{–3}$; Gas jet diameter $D$, dimensions $L$ and air density $\rho$, dimensions $ML^{–3}$
The variables form a non-dimensional product $k$
$k = L^a\cdot P^b\cdot D^c\cdot \rho^d$  where $a,b,c,d$ are numbers to be determined.
Let’s form now a parallel product $k^*$ with the dimensions:
$k^* = (MLT^{–2})^a  (ML^2T^{–3})^b  (L)^c (ML^{–3})^d$
Clearly, $k^* = M^0 L^0 T^0$... We now take the exponents for each dimension:
$a  + b + d = 0 \\
a + 2b + c – 3d = 0 \\
–2a – 3b = 0$
We make $a = 1$, since $L$ is the variable we’re going to solve for.
$b = –2/3 \\
d = –1/3 \\
c = –2/3$
Then,
$k = L^a\cdot P^b\cdot D^c\cdot \rho^d \rightarrow  k = L\cdot P^{–2/3}\cdot D^{–2/3}\cdot \rho^{–1/3}$
Solving for $L$
$L = k\cdot P^{2/3}\cdot D^{2/3}\cdot \rho^{1/3}$
where $k$ is a constant
Hence, for gas jet diameters $D_1$ and $D_2$, and for the same power and air density, the corresponding values of thrust $L_1$ and $L_2$ are:
$L_1/L_2 = (D_1/D_2)^{2/3}$
For the case of $D_1 = 400 mm$ and $D_2 = 200 mm$, $L_1/L_2 = (400/200)^{2/3} = 1,59$
In other words, the larger (400 mm) gas jet gives you, for the same absorbed power and air density, 59% more thrust than that attained with the smaller (200 mm) jet.
Of course, this is an approximation valid for not too high aircraft speeds, based upon momentum theory, but gives you an idea...  For different values of power and gas jet diameter, you can derive the constant k from the data of thrust, power and diameter you already have,  $k = L\cdot P^{–2/3}\cdot D^{–2/3}\cdot \rho^{–1/3}$  and then use that constant in your calculations.

Probably worth noting here that a large fan can readily be designed to absorb much more than the same amount of power -- double diameter = 4x area, could be roughly 60 kW in this case.  Using four motors geared together would be the simple way...

@xxavier wow, thanks for your great answer! An equation to roughly estimate thrust is exactly what I needed.

@Zeiss Ikon Yes, that‘s a question I asked myself, too. In case I wouldn‘t just double the diameter and put in the same power but doubled or quadroupled the power either, what potential thrust could such an EDF produce ?

According to the math in the answer above, doubling the power will approximately double the thrust, providing your fan can absorb the additional kW.  Looks like you could get as high as roughly 6x the original, if you can supply 60 kW.  That's an hour's duration on the top-end battery from a 2018 Nissan Leaf, if you can keep everything cool...

I dont have much to add but I would just like to say kudos for one of the clearest and easy to understand examples of Buckingham-Pi dimensional analysis I've ever seen.

Simple impulse theory equations for thrust T and power P:
$$T = C_T \cdot \rho A (\Omega R)^2$$
$$P = C_P \cdot \rho A (\Omega R)^3$$
Both scale linearly with disk area A. At constant tip speed $\Omega R$ and thrust/power coefficients, the scalings are simply T = $k_T A$ and P = $k_P A$ with $k_T$ and $k_P$ constants.
So a 400 mm fan would produce (400/200)$^2$ = 4 times the thrust, at 4 times the power. Note that the larger fan has lower RPM, in order to maintain constant tip speed.

Order Of Magnitude check: the four listed electric fans. The largest and the smallest fan have lower P/A, a matter of available electric motor size?

From the data table of the fans, a mean value of k = 1.08 can be calculated. A good agreement for the thrust L as a function of diameter D and power P is obtained inserting it in the dimensionally derived expression
$L = k\cdot P^{2/3}\cdot D^{2/3}\cdot \rho^{1/3}$   With caution, that expression can be used for other particular cases...


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What are the abilities and limits of a hexapod-based flight simulator?

So, that's a professional hexapod- a. k. a. Stewart platform-based flight simulator (image source: Wikipedia - "Stewart platform").  By moving the simulated cockpit, it simulates the movements of a plane during its maneuvers.
But the range of maneuvers it can realistically simulate is certainly limited - it can certainly simulate a straight flight, but I doubt it can give its occupants the realistic impression of a full barrel roll.
Given an existing, recent (i. e., modern and advanced) siulator for commercial aviation:
What are the actual limits on maneuvers and their parameters (i. e. turn and turn radius, banking and bank angle)?
Bonus question: How does this compare to the flight situations encountered in a typical flight?

What they can do.
Motion systems can produce accelerations that stimulate the acceleration sensors in our inner ear. Higher frequency acceleration can be sensed instantaneously in surge, sway and heave. From this answer:

Motion systems can do a pretty good job at reproducing direct accelerations, until the actuator stroke runs out of course. So for short term accelerations.

This direct acceleration sensing is essential for pilot-in-the-loop motion control, that is why we have the sensors in the first place. The velocity information we get from our peripheral vision is an integrated signal and has 90° phase shift, causing a delay in sensing of motion.
What they cannot do.
Produce sustained accelerations. Six Degree of Freedom motion systems get by by tilting the sim, so that a component of gravity can be used for the feeling of sustained motion. But with some restraints on tilt velocity and angle, the tilt must happen imperceptibly and is of course also limited by the actuator stroke:

Imperceptively, by rotating at a rate below what the inner ear sensors can detect, and by not changing the visual image horizon.
Limited by stroke: in a 6-DoF system, using full tilt means that some of the other DoFs cannot be used. Full aft tilt has the front actuators fully extended, so linear surge cannot be actuated anymore.

Motion software contains a lot of fine balancing and frequency filtering code, to make optimal use of the available stroke and of the peculiarities of the inner ear acceleration sensors. Large stroke systems are essential for pilot-in-the-loop tasks in airliner and helicopter pilot training, and make the difference between being in an immersive simulated atmosphere, or being aware of the fact that you're inside some device firmly on the ground.

It's not restricted - the sim will continue to move through any maneuvers - but realism degrades the further away they get from zero.
Full-motion simulators don't map motion 1:1, but rather trick the senses. Maneuvers are performed with velocity and acceleration. What the human body senses is acceleration. And what the brain processes most actively is jerk - the rate of change of acceleration.
This means that, if you want to simulate the bank in a 360-degree barrel roll, you just need to simulate the initial jerk from initiating the roll. Say it's 10 deg/s^3 for 2 seconds to initiate the roll, then -4 deg/s^3 for 5 seconds as it stabilizes. But if you do 8 deg/s^3 for 1.5 seconds to initiate and -3 deg/s^3 for 6 seconds to stabilize, the human inside won't know the difference.
So that's what you do. The sim cabin jerks almost as much as a real plane, but the acceleration ceases sooner than it would in reality, and where the real plane would've been stable, the sim cabin will gradually return to its neutral point.
The effect of motion on a collimated surround display is immersive enough that first-time visitors often mistake a simple static sim for a motion one. Actually adding a bit of motion, then slowly returning it to neutral after every maneuver, completes the illusion.
You don't have to simulate the entire motion, just hint at it enough to corroborate the information the pilot's brain gets from the picture.

It's not really "unlimited" though. This type of sim can present a wide range of sensations, but try sustained inverted flight in one. "g" will never point up...

@RonBeyer Inverted level flight is perhaps the one thing that can't be simulated at all, because the direction of lift changes. Inversion in a barrel roll, on the other hand, is within type 7 simulators' capabilities.

Straight climb, straight dive, knife edge, etc.... Those are things this simulator cannot do. Any maneuver that causes "G" to be outside the limits of tilt. It also cannot simulate more than 1g (at least not for more than a second or so), for example in a level turn with 45 degrees of bank. There are a lot of things that this simulator can't do, not just inverted flight. These simulators are good for certain envelopes, but they can break down outside those physically speaking.

@RonBeyer Level turn with bank simulation works acceptably. The platform simulates the initial transition to the bank quite well, and then returns to 1g. Which doesn't matter, because you aren't going to get 7g turns, the kind that make you unable to lift your arms and black out intermittently, and thus would have to be simulated, in a transport aircraft. The purpose of the platform is to replicate the sensory cues that interfere with flying by the instruments, not to produce a perfect reproduction of everything you'd feel during an actual flight.


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Why is it necessary for pilots to have trim controls on fly-by-wire aircraft?
On Airbus family airliners why is it necessary for the pilots to have the facility to trim when there is no aerodynamic feedback through the flight controls?

You can find the answer in an answer to this question, it sounds like the computer takes care of it normally but its there in case of failure. I wont mark as dupe since you are asking a different root question but others may feel it is a dupe.

Yes I’m aware but I’m referring specifically to the Airbus sidestick which, forgive me if I’m wrong, has no bearing on the control surface deflection relative to its position

I don’t think it is strictly speaking necessary. It used to be the mechanical backup for FBW failures on early Airbusses, then it was kept a while for commonality. I am not sure whether the A350 still has it?

Airbus FBW aircraft have an Autotrim system, so the trim wheel is only there as a backup. In normal law, the trim system is invisible to the pilot. The sidestick pitch inputs control load factor, unlike in a yoke aircraft where it controls elevator deflection. This means that that the farther you move the stick forward and back the faster it pitches, but at center it is a zero load factor, so it stays at its current pitch angle.
As an example of the difference, if you want to pitch up 10° in a yoke aircraft you pull back on the yoke until it reaches 10° and hold it there. If you let the pressure off it will return to 0° unless you retrim for 10°. Whereas in Airbus normal law, to pitch to 10° you pull on the sidestick until it reaches 10° then let go. The FBW system automatically maintains the new pitch angle. If you don’t do anything else the FBW system will automatically trim the stabilizer to the new pitch angle. There is no feedback as to elevator deflection because it’s not directly controlling the elevator.
Pilot misunderstanding of the Autotrim function was a factor in the crash of XL Airways flight 888T. When the AoA vanes froze, the computer switched to Alternate 2 law, which does not have the Autotrim function. Due to the AoA fault, the autopilot had trimmed the aircraft full nose up. When the AP disconnected and control law degraded it remained there and notified the pilot that he needed to trim manually. The PF did not realize this, so never moved the trim wheel. With the stabilizer in full nose up trim he didn’t have enough elevator authority to prevent a stall and crashed into the ocean.

It's because on FBW aircraft the software is designed to mimic the behaviour of a mechanical system so that the instinctive pilot inputs will have a similar result.
Note that on any aircraft the trim control system is fundamentally a speed selector.  Also, airliners with hydraulic controls and moving stabilizers have no aerodynamic feedback (and the neutral position of the column doesn't change with trim changes) and you are just pulling and pushing against springs when you move the stick.
Trimming these airplanes is quite different to trimming an airplane with an elevator trim tab.  Trimming to a new speed requires that the column be displaced to pitch the airplane up or down and held there, then a trim input to move the stabilizer, then release some or all of the elevator input to see the result, then another trim input, release etc until the airplane is stabilized at the new trim speed with the control column at neutral.  It's a rapid tug/blip-the-trim/release/tug/blip/release/tug/blip/release process that becomes second nature once you figure it out (watch any cockpit video when the pilot is hand flying and slowing down during an approach).
A FBW system will mimic the same responses using software moving the elevator and stab so that the same instinctive pilot inputs will work and trim inputs change trim speed the same way.  Not sure about Airbus, but on the FBW C Series there is actually a trim speed bug on the primary flight display that tells you what your new trim speed will be when you make a trim input, taking away the guesswork zeroing in process when slowing down or speeding up.

Minor nit, but nothing about humans flying airplanes is "instinctive". It may be included in early basic training, and it may be something that pilots will fall back onto even under large amounts of stress, but it's not instinctive. If anything about flying airplanes was instinctive, then by definition no training would be required for that part of flying; no explanation would be required other than for illustrative purposes; and doing it any other way would require significant extra training.

You might be applying a bit too literal an interpretation.  It's common in English to use "instinctive" as a short hand to describe actions that are ingrained sufficiently by training/repetition/experience to be done without having to think about it.

@MichaelKjörling I completely disagree. There is a huge amount of human factors work that underlies flight control and dynamics. The aircraft is engineered so that a human can handle it. This includes things like control forces, damping and pilot-induced oscillations. The science of flight is inherently about control and stability, and the human is right in the middle of the loop. If you take a undergrad class on control theory, you find things like the number of poles in a control axis, the bandwidth of the system, and then how difficult it is for a human to stabilize the system.

@user you're thinking way too hard.  It was just a comment about the interpretation of a word, i.e., literal vs vernacular usage.

The trimmed position of the flight controls has different meanings for different control systems:

For manually controlled flight control surfaces, the flight controls trimmed position is the stick equivalent position that the control surface returns to when it is released, no hand or feet on the controls. The surface position where aerodynamic hinge moments are zero.
For hydraulically operated irreversible control surfaces, the stick trim position is an offset to the artificial feel spring - the position that the stick feel spring returns to when released. Notice that some irreversible systems have Q-feel: feel springs that change their spring stiffness as a function of dynamic pressure. The B737 has such a system.

In both cases, whether the aeroplane remains in a trimmed state of flight (no heading or altitude change) once the stick is released depends on where the zero force position is located. This location needs to be set by the pilot, via the trim switches or trim wheels, which set the position of the trim tabs or stabilisers.
In the A320, there is an artificial feel spring loading the stick as well. The only difference with the artificial feel spring system of an irreversible hydraulic actuation system, is that the zero force position never changes, and that in normal mode this is also the aeroplane trimmed position.
In degraded modes there is no automatic trimming of the flight state, and the pilot needs to operate the trim wheel in order to set the stabiliser angle. This is also the backup pitch control mechanism for when all hydraulics are off.


text:
Are fully electric helicopters suitable for military operations?
I read this question about diesel-electric (DE) helicopters, which sparked the following question:
Are fully electric helicopters suitable for military operations?
They are more silent, and electric motors are lighter than combustion engines. Would the only drawback be battery weight?

@CGCampbell Two of them: the transmission won't be necessary either.

Battery weight alone isn't enough of a drawback?

I'd be very interested in that electric motor which is lighter than a combustion engine (which in helicopters is very often a gas turbine). Where can I get one?

Fully electric helicopters would be much more silent indeed: turbines are incredibly noisy, and the gearbox is another source of noise that would not be present since electric motors don't require one. Use a many bladed rotor with swept tips and high aspect ratio blades, and rotor noise would be reduced as well.
They would also have a short range and a small payload capacity, since a lot of it is used for lugging batteries around. Weight is a serious issue for aircraft in general and helicopters in particular: vertical flight can use very little aerodynamic L/D leverage effect. In vertical flight, thrust = weight.
A hybrid helicopter would reduce battery size: a turbine plus generator provides electricity for the electric motor and charges the battery. When within range of the target, the turbine is shut down and the helicopter continues forward flight and landing on the batteries. Extra weight compared to conventional would be the electric motor + generator + batteries, weight saving = transmission. Eject the spent batteries on the way home for increased range.

From the perspective of someone on the ground, the engine & gearbox don't seem to contribute a significant amount of noise.  It's almost all the distinctive "thwop thwop thwop" of the rotor blades.  Also, in vertical flight, thrust > weight.  I once had an early toy electric helicopter which would fly ok in near sea level San Jose, but just sink at my ~5000 ft home.

Battery weight is a huge negative. Liquid hydrocarbon fuels have energy densities of about 45MJ/Kg, and the significant advantage that as you use them, their weight stops needing to be transported.
A lithium-air battery is theoretically capable of getting close to the energy density of hydrocarbon fuels, but the best that's been achieved so far in the lab is about 6MJ/Kg. The energy density of lithium-ion batteries, which are the best that's deployable at present. are more like 1MJ/kg, at the cell level, or rather worse at the pack level. If you want to drop used batteries, your operating costs go way up.
And while electric motors might be lighter than piston engines, they are heavier than gas turbines, which are the dominant form of power for helicopters, especially military models.
An electric helicopter could be built, but its flight duration would be very short. Just like quadcopter drones.

Also, the question starts with a wrong proposition: Electric engines are heavier than comparable combustion engines; in that case gas turbines.

@PeterKämpf: Thanks, added.


text:
How is an off-field landing accomplished at night?
Common sense suggests it's much easier to do an off-field landing at day than at night, curious to know how it's accomplished at night.

What aircraft type are you interested in? Helicopter? Glider? etc.

Joke: The procedure is as follows; descend to 50ft. Switch on your landing lights, if you like what you see, land, if not switch off landing light.

Aim for a dark patch and hope there are no trees, power lines etc.

In the old days, mail planes used to carry parachute flares for use in such situations.  Maybe we ought to reinstate the practice.

Just make sure the highway is well-lit:  https://newyork.cbslocal.com/video/4941841-see-it-small-plane-lands-on-highway-in-minnesota/

It's much easier to do an off-field landing at night. Harder to use the aircraft again though...

Off-field landings at night are inherently more difficult and hazardous than in the day because depending on conditions you may have no way to tell what is down there. Unless you have decently strong moonlight all unlit terrain will be completely black, and you won't be able to tell forest from field. This is why it's critical to protect your night vision, it gives you a chance to see what's below you. If there's a highway down there that may be your best option, but if you're in a sparse area on a dark night you have to pick a spot that's into wind and hope it's not badlands. Even then it's still survivable if you have good technique, keep positive control of the airplane and reduce the airspeed as much as you can before impact, without stalling of course.
Aiming for clusters of lights sounds good at first, but that usually means buildings or parking lots which are not good choices.
The best way to de-risk this is through good flight planning. Choose a flight path that goes over friendly terrain: adding 15 minutes of flying time is worth it if it means you are over fields rather than rough terrain or water. Study the terrain using google earth or a similar tool. If you have a GPS you could even put good off-airport landing sites on your map. Give yourself extra altitude, and keep practicing your forced landing technique.

Ditto the flying at a higher altitude part. It will give you more time to reach a suitable landing area. Maybe even an airfield. In addition to careful flight planning, and protecting your night vision, I would add carrying supplemental oxygen to combat the increased oxygen requirements of your eyes at night.

That may be over the top, but worth considering if flying at higher altitudes. It's also dependent on health, age, physical fitness and whether someone's a smoker.

The FAA recommends supplemental oxygen above 5,000 feet MSL at night for that very reason. Depending on your Maximum Elevation Figure, you may have to consider flying as high as 10,000 feet (or at least the Minimum IFR Altitude) even when flying VFR at night. For the most part, this would still be below the FAA regulation required maximum without supp O2. But, it is still recommended that O2 is used.

I didn't know that @DeanF. Something to keep in mind for sure. I know there's small disposables you can get, given I live in the southeast of England where the highest point is about 1000ft it's not something I've given much thought about.

Then there's golf courses (just ask Harrison Ford).  Large, open field, mostly flat, few trees, not likely to be many people, often well-lit if they're used for tournaments.  (We're talking about small planes here, right?  Don't think a 747 could safely land in such a location.)

It's rare golf courses are lit, but if so they are a good choice. Only think a golf course is good for if you ask me @DarrelHoffman.

Only lit during during competitions that run late I'd imagine.

Chapter 10 of the FAA's Airplane Flying Handbook covers night emergency landings, here are some of the points it suggests (p. 10-9):

Maintain positive control of the airplane and establish the best glide configuration and airspeed. Turn the airplane towards an airport
or away from congested areas.
If the condition of the nearby terrain is known and is suitable for a forced landing, turn towards an unlighted portion of the area and
plan an emergency forced landing to an unlighted portion.
Consider an emergency landing area close to public access if possible. This may facilitate rescue or help, if needed.
Complete the before landing checklist, and check the landing lights for operation at altitude and turn ON in sufficient time to illuminate
the terrain or obstacles along the flightpath. The landing should be
completed in the normal landing attitude at the slowest possible
airspeed. If the landing lights are unusable and outside visual
references are not available, the airplane should be held in
level-landing attitude until the ground is contacted.

Having said all that, every situation is different. Checklists cover the 'mechanical' steps required to make an emergency landing but they can't tell you where to land. The pilot will always have to make that decision and it's a debate that comes up periodically on aviation discussion forums, especially about how close (or not) you should land to lights.

The landing should be completed in the normal landing attitude at the slowest possible airspeed.

What's the lowest possible airspeed on jet/turboprop having to do emergency landing considering reasonable issues for off-field landing?

@CupOfGreenTea I guess they mean "just above stall speed", and that depends on the aircraft type and configuration. A Cessna Caravan is a turboprop and stalls at a little over 60 knots, an airliner's stall speed would most likely be over 100 knots.

you have to love the ", if needed." - !


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How long is my first class medical certificate good for as a third class certificate?
My first class medical exam was on 01/07/2020. I am 64 years old. Is it now valid as a third class medical certificate until 01/31/2022?

Welcome to aviation.SE! I assume you’re asking about FAA regulations so  I added that tag to your question. For questions about regulations, please always mention the country or regulations that you’re asking about.

Is there a wrinkle to this question that I'm not seeing?  Because I would presume that someone in need of a first class med would know where to go for the answer.  Or do you just want someone else to look it up for you?  Lack of effort generally warrants a downvote...

You hold a First Class Medical Certificate, not a Third Class Medical Certificate.  As you are over the age of 40, the First Class Medical expires 24 calendar months after the date of issuance on your medical certificate, BUT ONLY IF you are conducting an operation requiring a recreational pilot, Private pilot, or Flight Instructor Certificate.  See §61.23(d)

Technically he has until January 2021 to exercise the privileges of a commercial pilot certificate.


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Is the FAA expected to issue more regulations soon on drone usage in rural areas?
There are exponential increases in funding for small drone startups.  When is the next publication period for the FAA to issue regulations on use of small drones in suburban areas?

Drones and Model Aircraft may be a good place for this question...

I think this site is a better place for this question.  It's not outside of the site guidelines, and if you look at Drones and Model Aircraft  SE, you'll see it's almost entirely about technical "what's the best way to do this" questions.

Your question is confusing. The title asks about "rural areas" while the body of the post asks about "suburban areas". The question already doesn't show any evidence of an attempt at research, but it's not even clear what you're asking.

I'm not sure if this is really an aviation question because you're asking about how and when Federal agencies make regulations, and you might get a better answer to that on law.SE.
But having said that, agencies are required to publish their rulemaking plans twice a year. You can find them in the "unified agenda" for that agency. If you look at the Department of Transportation agenda there are currently six FAA rules that include "unmanned aircraft" in their title. Four are already final, the other two are:

Safe and Secure Operations of Small Unmanned Aircraft Systems
Prohibit or Restrict the Operation of an Unmanned Aircraft in Close Proximity to a Fixed Site Facility

I haven't read them and I have no idea about the timeline for them or if they include anything about rural operations specifically.

The two that are not final are: https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2120-AL26 , https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2120-AL33.  Three that are final are https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2120-AK85 , https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2120-AL31 , https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2120-AL32 .  I must have missed one if four are final--


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What is the high pitched beep noise on A320s on startup?
Me and an engineer have been both breaking our heads over this, and no matter what we do we cannot figure this out. On certain A320 family aircraft, when the APU initializes/external power generator is turned on, there are a series of noises. First of course is the relay. Then there is the TR unit/alternator which makes a high pitched whine. But then there are a few differences which I do not understand.
In about half the videos of A320 startups, there is a high pitched single or double beep (videos attached below). I got told by some that it is the cockpit door lock/video system, others that it is the electrical system initializing, but nobody has a concrete answer to this.
Another thing, there are CIDS chimes when the aircraft gets powered. Strangely on some aircraft the CIDS chimes are slow and continuous once the battery is started. On others, once ext/apu power is on, there are two quick chimes and nothing when batteries are on
If someone knows for sure what this is, please do tell me, because me and the engineer would really appreciate knowing this, there are a few variations of the sounds I have heard.

 has a single beep double chime,

 has a double beep then continuous chime, and lastly

 (3:18) has double beep, double chime.

Nice to see airbus crowd sourcing it's troubleshooting ;)


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What is the Mach Never Exceed number for a C-130J Hercules under ISA conditions (approximations are welcomed!)
I am looking for the Mach Never Exceed number for a C-130J Hercules so that I can create an approximate 1g envelope.
Does anyone have any idea what this can be? I am trying to find the value for similar aircrafts so that I can make an educated approximation but I am having no such luck. Perhaps someone with more experience can provide me with an educated estimation.
Thanks!

The MMO for a C-130J is Mach 0.77 according to flugzeuginfo.net. Official values will be found in the AFM for the aircraft and may vary between production variants of the C-130.

Thank you so much!


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What is the approximate thrust at sea level for a C-130J Hercules?
I am looking for the approximate thrust of a C-130J Hercules under ISA sea level conditions. Also the efficiency of its propeller would be of help.
An answer to this question would really help my calculations for an assignment, so I don't have to guess values. If you could direct me to your sources as well, that would be highly appreciated.
The C-130J is equipped with  Rolls Royce AE-2100 D3 engines and the propellers would be the 6-bladed Dowty R391.

Okay guys, so I found some data from an old service publication from Lockheed. It says that the new C-130J propulsion system under standard conditions and flying 80 kts is rated "4,637 SHP, but produces 10,200 lbs".
So using the equation for thrust available for a propeller aircraft I get:
$T_a = \frac{\eta \cdot P_s }{V}$
with:
$T_a = $Thrust available
$\eta =$propeller efficiency
$P_s =$shaft power
$V=$air speed
$\eta = \frac{T_a \cdot V}{P_s}$
$\eta = \frac{10200 \textrm{lbf} \cdot 80 \textrm{kts}[ \textrm{aka. }135 \textrm{ ft/s}]}{4637 \textrm{shp} [\cdot 550 \textrm{ conversion}]}$
$\eta = 0.54$
This seems quite low but its what I got for anyone wondering. The service publication I got the info from is this:
https://www.sikorskyaerospace.com/content/dam/lockheed-martin/aero/documents/sustainment/csc/service-news/sn-mag-v21-v30/V25N03.pdf

Since the propeller is optimized for higher speeds, this result looks about right.

Right! I was stuck on that! That would explain why its so low compared to my estimations. I was expecting something closer to 0.9, 80 kts is approximately its minimum velocity.

No, 90% is impossible with such a high disk loading. I would expect 82% to be the maximum at the design point.

Sir, if you have the time, could you briefly explain how you came to expect 82%? That seems like a relatively specific value. I assumed I could expect a high efficiency so that's why I guessed 90%. How do you know its not something like 75% or why didn't you round down to 80% for a more generalized answer?

It's only a guess. In the past I played around with Hamprop and would expect to get that number as a result. This would be without installation losses, e.g. from the higher friction on the surfaces in the prop slipstream.

Oh I see, thank you!


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Does a flight training company need to make a copy of my driver's license?
I want to get a Sport Pilot license, but the company that will train me wants to make a copy of my driver's license. I don't mind showing it, but is a copy required?

They usually want to keep a copy for legal purposes. they may ask for information to prove that you are a citizen and may be required to keep it on file.

Are you a US citizen?

Are you saying you want to get a Sport Pilot license because of identity theft issues? Or are you concerned about identify theft if the company retains a copy of your DL?

According to 49 CFR 1552.3 a flight school is required to keep a copy of the documents used to provide proof of citizenship for five years. This is usually a passport or birth certificate. A driver's licenses is not proof of citizenship in the US.
However, a valid photo ID (such as a driver's license) is required in addition to your pilot's license in order to exercise the privileges of the pilot's certificate because the FAA issued pilot's licenses do not have a photo for identification. So a business that is renting an aircraft to you has a legitimate interest in retaining evidence that they are handing over their valuable asset to a licensed pilot, and that you are who you say you are.
They may not be required to keep a copy of your driver's license, but they are also not required to rent you an aircraft or provide flight instruction.

"valid photo ID is required in addition to your pilot's license because the FAA issued pilot's licenses do not have a photo for identification" only while exercising the privileges of the pilot's certificate

@SteveKuo correct!

A driver's license does not establish citizenship, but does establish identity for TSA.  TSA has records requirements which instructors and schools must follow for flight training customers. Normally proof is provided by birth certificate or passport, and the school or flight instructor is required to keep a copy.  If  a birth certificate is used, a government issued photo ID is required, which is normally a driver's license, but does not have to be, if you have some other government issued photo ID (in my case I have an airport ID, which is photo ID issued by a local government).
To be clear, a driver's license does not serve the TSA citizenship documentation requirement.
However, FAA pilot certificates require photo ID for identification. For many people, a state issued driver's license is used.
Additionally, the school is entitled to keep records of certificates which you have, and in the case of sport pilot, the state issued driver's license acts as a medical certificate.
Finally, the school's insurance may require that certain records of students be retained. While that may not be a legal requirement, it is a practical one.

A drivers license does not establish identity in all states. The TSA only accepts drivers licenses from states that are REAL ID compliant


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What is the difference between Review and Analysis in DO-178C?
In the context of DO-178C, what is the difference between review and analysis of the outputs of the software development processes?
Are they both the same?

What part of this question required clarification for closure? DO 178 is clearly software requirement for airborne systems. For those who understand the question, it's perfectly clear. For those who don't, you have no business in closing this.

@JZYL agreed, users here seem pretty quick to close software certification questions as off topic pretty darn quick around here, and I don't get it.

No they are not the same.
Reviews are qualitative. They typically compare the artifact being reviewed to a standard using a checklist.
Analyses are quantitative. They could be functional analysis, data flow analysis, timing analysis, or other evaluation of the software artifact.
From DO-178C:

6.3 Software Reviews and Analyses
Reviews and analyses are applied to the outputs of the software
  development processes. One distinction between reviews and analyses is
  that analyses provide repeatable evidence of correctness and reviews
  provide a qualitative assessment of correctness. A review may consist
  of an inspection of an output of a process guided by a checklist or
  similar aid. An analysis may examine in detail the functionality,
  performance,  traceability, and safety implications of a software
  component, and its relationship to other components within the system
  or equipment.

@Gerry has provided a great answer. Let me complete it with a practical example, since conceptual reasonings regarding DO-178 might get most of the times mind-stressful.

Let's assume that we are developing an onboard Flight Control System SW which will be verified later.
On the one hand, SW will have to meet certain performance requirements (e.g. maintain level flight during in-air operations). However, due to the SW complexity, we cannot test by direct means (i.e. direct input and output) if this performance is met. But, we can carry out more tedious tests and analysis, such as simulations, in order to verify it.
On the other hand, during the SW development, we have created several design diagrams (e.g. modules, class decompositions, functions, etc.). The verification of these designs could be done by a simple review between the design documentation and the actual SW architecture.


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Do airline pilots increase thrust when ordered to increase altitude by traffic controllers?
Do airline pilots increase thrust when ordered to increase altitude by traffic controllers?  Do they simply use flaps, the yoke (or joystick in the case of airbus) and the stabilizers without any increase in thrust.  What is the altitude increase sequence or procedure .  Do they simply rely on auto pilot and if so does it increase thrust too?

well, ATC hardly ever ‘orders’ pilots to do something, but if they did: how would expect to climb without adding thrust? trading speed for altitude would be a method, but it won’t get you very high. altitude, like speed, is energy and that energy has to come from somewhere

@Radu094 ' it won’t get you very high' It would actually. If you (temporarily) reduce speed, you have energy to spare for climbing. Drag goes up quadratically with speed, so if you reduce speed by 30%, you can use half the energy of your engines for climbing.

well, it depends on what side of the drag curve you are, mind you, (as reducing speed will increase induced drag) but I see your (valid) point. I was only talking about trading kinetic vs potential energy (eg like a glider) which is not giving you much altitude

Do airline pilots increase thrust when ordered to increase altitude by traffic controllers

Yes, without increasing thrust the act of ascending would reduce speed.

Do they simply use flaps

No, flaps are not used to climb. They are used to increase the surface area of the wing in order to allow the aircraft to fly at slower speeds (for example, during approach & landing).

What is the altitude increase sequence or procedure

Generally, and put simply, it is increase thrust then raise the nose.

Do they simply rely on auto pilot and if so does it increase thrust too?

They may well use the autopilot to do it all, but some autopilots do not control the throttle so that would be done manually by the pilot while the autopilot controls the rate of climb.

Almost all (or all) commercial airliners have an auto-throttle system, which is pretty much a part of the auto-pilot. If the pilot dials in a new altitude, the autopilot will pitch up and the auto-throttle will increase thrust to maintain speed.

@RonBeyer yeah, I guess my wording was bad there. I adjusted it.

I’ll try my hand at a more ‘scholastic’-aviation approach:
The normal procedure taught in flight school for initiating a climb is P-A-T.  That is Power-Attitude-Trim.

You increase power on the engine(s) first.If left alone, the plane will settle (very slowly, google phugoid) into a climb eventually
Because we do not want to wait the few mins or so it takes for the plane to settle into the climb, we use the elevator (via yoke or sidestick) to settle the attitude of the plane directly into a climb position (ie. point the nose higher up). A good pilot will do this without letting the speed climb or drop. ‘Call it pitch-for-speed.
Now the plane is in a different power/attitude and even though the plane is (or should be) at the same speed, a little bit of trimming is required to null the forces on the yoke.

now you can sit back and enjoy the climb.
Leveling off after the climb is a A-P-T.... you guessed: Attitude-Power-Trim.
The reasoning for the change of order is that you want to prevent the plane from a nose-up, low-power situation, with speed decaying quickly.
Mind you, in a modern airliner most of these things can be automated via an autopilot/autothrust as described in the other answers.

Most airliners today use auto pilot and auto thrust when flying in level flight or climbing and descending.
The normal sequence for a climb is to enter a new altitude in the flight computer and then engage a climb mode on the autopilot. In any aircraft thrust is usually increased for a climb and decreased for a descent. The Auto-thrust will adjust automatically in most modes to maintain a desired speed and rate of climb. The autopilot adjusts the elevator or stabilizer to climb or descend to the set altitude.

Hmm, sounds like you're having to work too hard. Why not just say, "Alexa, flight level 350" or whatever. LOL

@Terry "Now purchasing 350 flight levels to be sent to your home address"

@Terry: Why do you think voice input would be easier than just entering a new desired altitude?  Even apart from the problems posed by a noisy cockpit.

@jamesqf voice input is reserved for captains only.

@jamesqf I was just joking. I retired in 1999, and from my old fart standpoint, they've taken all the fun out of the job of being an airline pilot. My last 10 years was spent on 747-100/200s with a 3-man crew and no so-called glass cockpits. When assigned a higher altitude, we dialed (actually turned a physical dial) the new altitude into a little window of rotating digits for reference. Then the flying pilot would disengage the autopilot and ask the f.e. to set climb power. Reaching the new altitude, he'd engage the autopilot with altitude hold and ask the f.e. for cruise power.

@kevin Of course! That's the way it should be.

@ZachLipton That was good for the best laugh I've had in quite a while!

@Terry Given only that, how would Alexa know whether to climb, descend or maintain altitude? I mean, sure you'd know, but Alexa...

@MichaelKjörling First you would say, "Alexa, order one complete Alexa autopilot interface for this airplane." There would be a pause, and Alexa would reply, "Sorry, the charge for that is several thousand times greater than your credit card limit. Would you like to try PayPal?"


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Can an aircraft be stalled at low altitude and safely land on water?
P.S Its just a random question...please consider the fact I have zero knowledge of aerodynamics of a plane.

Related: https://aviation.stackexchange.com/questions/44740/why-cant-you-ditch-your-aircraft-in-the-sea You can't land an aircraft with zero forward airspeed; so the 'safely' depends on how low the stall speed is.

That is the normal procedure for water landings with land airplanes. You fly parallel to the water as low as possible until the flight speed is too low to carry the full weight of the airplane. If it can be done safely, however, depends on a lot more than only the landing technique. Some aircraft will not swim and the drag of the landing gear might cause the aircraft to topple over.

Isn't every landing a stall? Maybe only in the last seconds but it will be a stall. In the end the stick is pulled back such that the nose raises and the wings create an air cushion with the ground on which the aircraft "falls" down on the main landing gear.
For water landings it is essential that drag components, like engines, wheels etc, touch the water symmetrically, so left and right at the same time which will keep the aircraft in a straight line instead of turning and topple it over

@Brilsmurfffje: No, at some point the wheels carry over without the wing stalling. The best landings are imperceptible except for the wheels spinning up. Details depend on the stall behavior - some aircraft show a clear lift drop in a stall and would produce a bump when the wings refuse to carry all the lift and the aircraft drops on its wheels.

opinions differ but a technically good landing is one that you can feel as both rear wheels toch down firmly and only once. A very soft landing is also not preferably as it can result in more wear on the tires, since they touch the groundly only slightly before the final touchdown. This result in 2 times up spinning the tire.

@Brilsmurfffje: Do you have any references or more arguments for that idea? It also came up a few weeks ago, and i am not quite convinced. I don't see why there would be more wear if the tires spin up slowly, it wil surely be more even though. I don't think the tires will have much time to slow down again if they spin up in two steps.

@rickboender, "slowly" upspinning will smear the rubber over a longer distance on the runway. With crosswinds you also want a firm touchdown as it reduces the skidding over the runway and thus the wear on the tires. If you look up pictures on the internet of runways were mainly 737's land you will see longer and shorter black lines indicating smooth and firm landings respectively.


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Performance Calculation with upgraded engine
I have an upcoming checkride and the DPE has asked to plan a cross country flight.  The aircraft that will be used is a PA28-151; however, it has an upgraded 160hp engine.  Regarding performance calculations, should I use charts from the current -151 PoH or can I use a charts from a similar model -161 PoH?

How did you plan your previous cross countries (if any) in the same aircraft?

I usually use foreflight and don’t fly too far but the examiner will probably want planning performed manually.

The engine upgrade requires an STC. The STC should have included a flight manual supplement with updates to affected procedures, operating limitations and performance data. It won't be found in 'generic' manuals. You'll need to look at the manual in the aircraft.


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Maximum Flaps extended speed Vfe for full or partial flaps?
I fly Piper Archer/Warriors and the POH states "Maximum Flaps Extended Speed (VFE) – Do not exceed this speed with the flaps extended."  I try not to but I occasionally may exceed Vfe with one notch of flaps during a descent.  Could there be structural damage to the flaps in time or do aircraft designers factor in such potential pilot errors?

Yes they do, within reason.  Covered by my answer here: https://aviation.stackexchange.com/questions/69857/is-it-right-to-extend-flaps-only-in-the-white-arc/69858#69858

You're descending at above 103 KIA with flaps extended in a PA28? Why? Slow down or retract the flaps!

VFE is calculated for full flap extension, so the loads with just one notch of flaps are much smaller than the limit loads which determine VFE. It is very unlikely that this results in structural damage. Having said that, there is really no reason to exceed VFE with flaps down.
There are two types of damage that could result from flying too fast with flaps extended. The flaps or their attachments could be overloaded, or the wing loads in a vertical gust might exceed the strength of the wing. Both should be avoided.

On large aircraft, there are separate Vfe for different flap extensions.

@Jimmy: Yes, and the question is about a PA-28. FYI: This is a small GA aircraft. Wikipedia even has an article on it, complete with specs.

Unless a different speed is explicitly noted for partial flap extension, Vfe pertains to extending the flaps any amount. (For example, the C-172RG has a Vfe of 130 KIAS to 10º flaps, 100 KIAS beyond 10º flaps. Not so for the PA28s.)


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Glidepath difference
I recently flew an RNAV/LPV instrument approach in IMC.  Although out of the clouds by then, I was watching my vertical guidance on my NAV (which was at center) and noticed I was below glideslope for the visual PAPI.  Are my instruments wrong or does LPV and Visual Glide Slop Indicator (VGSI) really have a difference in glide path?

Which approach?  (some specifically mention it if they aren't coincident.)

It may also help to specify the airport and the type you were flying. PAPI lights are often calibrated for the sort of aircraft common at an airfield

It is not uncommon for the glide path for an instrument approach to differ from the visual glideslope.  This is generally noted on the approach plate.
You can see this in the example below where just above the profile view there is a note stating:  “VGSI and RNAV glide path not coincident. (VGSI angle 3.00/TCH 55)”.


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How does the capacity of 2 parallel runways compare to single runway?
Under IFR, what is the capacity of 2 near parallel runways and how does it compare to mixed mode single runway?

When a aircraft takes of and land on a single runway, the runway is operating at mixed mode.
I am asking about maximum aircraft operation on a mixed mode single runway, vs a near parallel runway under IFR. Under IFR rule for near parallel runway, one is dedicated for landing and the other for take off.


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What does ATC do during "slow" times?
I know at larger airports, it's NEVER a slow time. But what about at smaller airports that are large enough to rate manned ATC, but things aren't always fast-paced, high-traffic like at JFK or DFW, etc. (say an airport like JLN (Joplin Regional))?
What other duties do ATC personnel do when the traffic is light? Do they just sit and stare all day at the readouts, waiting for any one aircraft to appear and call in? Or are there other "busy work" items they do when things are 'slow' and they are listening for air traffic to call in for instructions?

They can be quite talkative at times, especially at night, even at busy places like Boston, MA, which is quite a large east coast airport.

Sleep. https://www.bloomberg.com/news/articles/2011-03-24/reagan-airport-gets-second-night-controller-on-sleep-concerns

"If you've got time to lean, you've got time to clean!" ;-D

@JScarry: indeed, scary  but one of the two controllers in the tower was taking a break in the 2002 Überlingen midair collision (https://en.wikipedia.org/wiki/2002_Überlingen_mid-air_collision#Other_factors_in_the_crash)

Learning to play a new musical instrument is often a good option.

Admin stuff, emails, chat with a colleague if you are not alone on shift, read up on (ever changing) procedures, eat, read a book, make sure the coffee machine works, meditate, watch TV. Anything goes, really, as long as you keep an eye on the radar and stay close enough to hear the radio and answer the phone. Of course, this is all assuming that there are literally no aircraft in the sector at that time (which happens regularily at smaller airports). Whenever you have any active aircraft, you obviously need to stay quite focused on that.

I think there's an important unsaid bottom line: You need to be able to switch back to "fully focused" within a second, no matter what you were doing.

@yo' That's very true

Traffic is fairly predictable. They operate with more personell during rush hour and with much less at night, so it rarely happens that a controller is idling.
During peak times there are separate controllers for apron operations, clearance delivery, taxiing, takeoffs and landings, arrivals, departures and for each en-route sector. During slow times, a single controller handles multiple roles or sectors.
Sometimes ATC is so understaffed at night that a controller might be more busy than during the day. For example, the Überlingen mid-air collision was caused by the lone controller beeing overwhelmed by simultaneous events on two workstations that would normally be operated by two people.

My primary airport is staffed 6a-10p, but when the weather is below VFR mins, they can go hours between planes because the flight schools aren't flying and most transient IFR traffic prefers airports closer to the city.

In the center environment, when sectors within a given area of responsibility are slow, they can be combined so a radar team can work a larger proportion of the airspace. Controllers who are not working traffic may be on break, or they may be assigned other duties, such as reading up on new procedures, letters of agreement, general aviation notices, and the like. There's ALWAYS something to get caught up on, and much of it is required before signing on to a position.
In the olden tymes, most of us would arrive 5 to 10 minutes before the shift started, and catch up the mandatory reading, get a weather briefing, and look at the flows for Denver, so you'd have a general handle on what to expect. We'd do that BEFORE shift start.
Can't do that anymore, because of contract negotiations. FAA has to provide time-on-the-clock for required items.
expeditedescent's answer illustrates some of the differences between Tower/TRACON/Center, though. In the center (at least ZDV), you cannot have anything in the area that would be a distraction to working traffic. No TV, no books, no magazines (not even aviation related), games, etc., except FAA-issued orders and the like. If you're not assigned a position (or just coming in/going out), you normally shouldn't be in the area, unless you're doing some approved activity (discussing PTO, new procedures, etc.)


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What is the 'end plate' effect?
When talking about T-tail configuration, I don't understand the statement that, "The vertical tail can be shorter due to the end plate effect of the horizontal tail."
What exactly is the endplate effect and how does it affect the aerodynamic characteristics of the tail?

An end plate on a lifting surface (which the vertical tail is, during a yaw maneuver) reduces tip vortex formation, which means less lifting area is needed to produce the same lift force.  It also significantly reduces induced drag, though the parasitic drag of the plate is usually a net loss unless, as in the case of a horizontal tail, the "plate" serves some other function that would be required anyway.
Whitcomb and newer design winglets use careful design to give similar effects with less, or even negative drag -- but you'd need a horizontal tail anyway, so the reasons not to have a T configuration boil down to structural weight, elevator blanketing in a stall, and control routing issues.
For an example of an aircraft that makes good use of tip plates to allow a shorter wingspan, look up the Bumblebee -- at least at one time, it was the dimensionally smallest piloted aircraft ever flown, and it critically depended on tip plates on both upper and lower wings to produce enough lift to fly.

The bumblebee stalled at close to 90 mph.  The little tip plates did nothing significant.  For tip plates to do any good they have to extend at least half a chord away from the wing surface.

Apparently the designer of the Bumblebee thought there was some benefit, else he'd have used some other termination for the wings.

Another end plate application is putting the vertical
stabilizers on the end of the H stab!  This would make
the elevator more effective by "trapping" higher air
pressure when the elevator is deflected.  Essentially
a type of fence.  This also showed up on the XB-70
when it's wing tips folded down to ride its own shock wave.  Also seen on wing tip tanks.  But, as it creates drag, the trick is to combine it with another
function.  Birds seem to do a great job doing this with their outer wing tip feathers, combining slats,
winglets, and vertical stabilizers all in one.


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Did the "feeler" ailerons of the B-52A-F make air-to-air refueling easier than with the B-52G/H?
The B-52G/H uses 8 spoilerons (so it has 8 burning and 8 turning on its wing) and a shortened vertical stabilizer.  Spoilerons seem to be very effective for this design, further reducing the need for a conventional rudder and ailerons to yaw and roll the aircraft.
The B-52A through B-52F had what have been described as "feeler ailerons".  But their elimination meant that the aircraft no longer has pure roll control, making maneuvering up to a tanker a bit more cumbersome, as inputs from the spoilerons would swing the nose from side to side.
It did occur to me that the tanker, and its boom, would do most of the adjusting, but was the "D" easier to handle in these situations? A response from someone with actual experience would be greatly appreciated.

You expect to find a B-52 driver here?  In any case the yaw damper system would account for any pro-verse yaw from roll spoilers so I don't think that's an issue.  As well, in formation flying in tight quarters, you use very small mounts of skid to maintain lateral station, not bank.

The B-52G/H only has 14 spoiler panels, 7 on each wing.